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Arachidonate 12-lipoxygenase, 12R type, also known as ALOX12B, 12R-LOX, and arachiconate lipoygenase 3, is a lipoxygenase-type enzyme composed of 701 amino acids and encoded by the ALOX12B gene.[1][2][3][4] The gene is located on chromosome 17 at position 13.1 where it forms a cluster with two other lipoxygenases, ALOXE3 and ALOX15B.[5] Among the human lipoxygenases, ALOX12B is most closely (54% identity) related in amino acid sequence to ALOXE3[6][7][8]


ALOX12B oxygenates arachidonic acid by adding molecular oxygen (O2) in the form of a hydroperoxyl (HO2) residue to its 12th carbon thereby forming 12(R)-hydroperoxy-5Z,8Z,10E,14Z-icosatetraenoic acid (also termed 12(R)-HpETE or 12R-HpETE).[2][3] When formed in cells, 12R-HpETE may be quickly reduced to its hydroxyl analog (OH), 12(R)-hydroxy-5'Z,8Z,10E,14Z-eicosatetraenoic acid (also termed 12(R)-HETE or 12R-HETE), by ubiquitous peroxidase-type enzymes. These sequential metabolic reactions are:

arachidonic acid + O2 12R-HpETE → 12R-HETE

12R-HETE stimulates animal and human neutrophil chemotaxis and other responses in vitro and is able to elicit inflammatory responses when injected into the skin of an animal model[9][10] However, the production of 12R-HETE for this or other purposes may not be primary function of ALOX12B.

ALOX12B is also capable of metabolizing free linoleic acid to 9(R)-hydroperoxy-10(E),12(Z)-octadecadienoic acid (9R-HpODE) which is also rapidly converted to its hydroxyl derivative, 9-Hydroxyoctadecadienoic acid (9R-HODE).[11]

Linoleic acid + O2 9R-HpODE → 9R-HODE

The S stereoisomer of 9R-HODE, 9S-HODE, has a range of biological activities related to oxidative stress and pain perception (see 9-Hydroxyoctadecadienoic acid. It is known or likely that 9R-HODE possesses at least some of these activities. For example, 9R-HODE, similar to 9S-HODE, mediates the perception of acute and chronic pain induced by heat, UV light, and inflammation in the skin of rodents (see 9-Hydroxyoctadecadienoic acid#9-HODEs as mediators of pain perception). However, production of these LA metabolites does not appear to be the primary function of ALOX12B; ALOX12B's primary function appears to be to metabolize linoleic acid that is not free but rather esterified to certain[citation needed]

Proposed principal activity of ALOX12B

ALOX12B targets Linoleic acid (LA). LA is the most abundant fatty acid in the skin epidermis, being present mainly esterified to the omega-hydroxyl residue of amide-linked omega-hydroxylated very long chain fatty acids (VLCFAs) in a unique class of ceramides termed esterified omega-hydroxyacyl-sphingosine (EOS). EOS is an intermediate component in a proposed multi-step metabolic pathway which delivers VLCFAs to the cornified lipid envelop in the skin's Stratum corneum; the presence of these wax-like, hydrophobic VLCFAs is needed to maintain the skin's integrity and functionality as a water barrier (see Lung microbiome#Role of the epithelial barrier).[12] ALOX12B metabolizes the LA in EOS to its 9-hydroperoxy derivative; ALOXE3 then converts this derivative to three products: a) 9R,10R-trans-epoxide,13R-hydroxy-10E-octadecenoic acid, b) 9-keto-10E,12Z-octadecadienoic acid, and c) 9R,10R-trans-epoxy-13-keto-11E-octadecenoic acid.[12][13] These ALOX12B-oxidized products signal for the hydrolysis (i.e. removal) of the oxidized products from EOS; this allows the multi-step metabolic pathway to proceed in delivering the VLCFAs to the cornified lipid envelop in the skin's Stratum corneum.[12][14]

Tissue distribution

ALOX12B protein has been detected in humans that in the same tissues the express ALOXE3 and ALOX15B viz., upper layers of the human skin and tongue and in tonsils.[5] mRNA for it has been detected in additional tissues such as the lung, testis, adrenal gland, ovary, prostate, and skin with lower abundance levels detected in salivary and thyroid glands, pancreas, brain, and plasma blood leukocytes.[5]

Clinical significance

Congenital ichthyosiform erythrodema

Deletions of Alox12b or AloxE2 genes in mice cause a congenital scaly skin disease which is characterized by a greatly reduced skin water barrier function and is similar in other ways to the autosomal recessive nonbullous Congenital ichthyosiform erythroderma (ARCI) disease of humans.[13] Mutations in many of the genes that encode proteins, including ALOX12B and ALOXE3, which conduct the steps that bring and then bind VLCFA to the stratums corneum are associated with ARCI.[15][16] ARCI refers to nonsyndromic (i.e. not associated with other signs or symptoms) congenital Ichthyosis including Harlequin-type ichthyosis, Lamellar ichthyosis, and Congenital ichthyosiform erythroderma.[12] ARCI has an incidence of about 1/200,000 in European and North American populations; 40 different mutations in ALOX12B and 13 different mutations in ALOXE3 genes account for a total of about 10% of ARCI case; these mutations uniformly cause a total loss of ALOX12B or ALOXE3 function (see mutations).[12]

Proliferative skin diseases

In psoriasis and other proliferative skin diseases such as the Erythrodermas underlying lung cancer, cutaneous T cell lymphoma, and drug reactions, and in Discoid lupus, Seborrheic dermatitis, Subacute Cutaneous lupus erythematosus, and Pemphigus foliaceus, cutaneous levels of ALOX12B mRNA and 12R-HETE are greatly increased.[5][17] It is not clear if these increases contribute to the disease by, for example, 12R-HETE induction of inflammation, or are primarily a consequence of skin proliferation.[12]


The expression of Alox12b and Aloxe3 mRNA in mice parallels, and is proposed to be instrumental for, skin development in mice embryogenesis; the human orthologs of these genes, i.e. ALOX12B and ALOXE3, may have a similar role in humans.[12]

Essential fatty acid deficiency

Severe dietary deficiency of polyunsaturated omega 6 fatty acids leads to the essential fatty acid deficiency syndrome that is characterized by scaly skin and excessive water loss; in humans and animal models the syndrome is fully reversed by dietary omega 6 fatty acids, particularly linoleic acid.[18] It is proposed that this deficiency disease resembles and has a similar basis to Congenital ichthyosiform erythrodema; that is, it is at least in part due to a deficiency of linoleic acid and thereby in the EOS-based delivery of VLCFA to the stratum corneum.[12]


  1. "Entrez Gene: ALOX12B arachidonate 12-lipoxygenase, 12R type".
  2. 2.0 2.1 Boeglin WE, Kim RB, Brash AR (June 1998). "A 12R-lipoxygenase in human skin: mechanistic evidence, molecular cloning, and expression". Proceedings of the National Academy of Sciences of the United States of America. 95 (12): 6744–9. Bibcode:1998PNAS...95.6744B. doi:10.1073/pnas.95.12.6744. PMC 22619. PMID 9618483.
  3. 3.0 3.1 Sun D, McDonnell M, Chen XS, Lakkis MM, Li H, Isaacs SN, Elsea SH, Patel PI, Funk CD (December 1998). "Human 12(R)-lipoxygenase and the mouse ortholog. Molecular cloning, expression, and gene chromosomal assignment". The Journal of Biological Chemistry. 273 (50): 33540–7. doi:10.1074/jbc.273.50.33540. PMID 9837935.
  5. 5.0 5.1 5.2 5.3 Schneider C, Brash AR (August 2002). "Lipoxygenase-catalyzed formation of R-configuration hydroperoxides". Prostaglandins & Other Lipid Mediators. 68–69: 291–301. doi:10.1016/s0090-6980(02)00041-2. PMID 12432924.
  6. Klein A, Pappas SC, Gordon P, Wong A, Kellen J, Kolin A, Robinson JB, Malkin A (February 1988). "The effect of nonviral liver damage on the T-lymphocyte helper/suppressor ratio". Clinical Immunology and Immunopathology. 46 (2): 214–20. doi:10.1016/0090-1229(88)90184-5. PMID 2962793.
  7. Bylund J, Kunz T, Valmsen K, Oliw EH (January 1998). "Cytochromes P450 with bisallylic hydroxylation activity on arachidonic and linoleic acids studied with human recombinant enzymes and with human and rat liver microsomes". The Journal of Pharmacology and Experimental Therapeutics. 284 (1): 51–60. PMID 9435160.
  8. Buczynski MW, Dumlao DS, Dennis EA (June 2009). "Thematic Review Series: Proteomics. An integrated omics analysis of eicosanoid biology". Journal of Lipid Research. 50 (6): 1015–38. doi:10.1194/jlr.R900004-JLR200. PMC 2681385. PMID 19244215.
  9. O'Flaherty JT, Cordes JF, Lee SL, Samuel M, Thomas MJ (December 1994). "Chemical and biological characterization of oxo-eicosatetraenoic acids". Biochimica et Biophysica Acta. 1201 (3): 505–15. doi:10.1016/0304-4165(94)90083-3. PMID 7803484.
  10. Fretland DJ, Anglin CP, Bremer M, Isakson P, Widomski DL, Paulson SK, Docter SH, Djuric SW, Penning TD, Yu S (April 1995). "Antiinflammatory effects of second-generation leukotriene B4 receptor antagonist, SC-53228: impact upon leukotriene B4- and 12(R)-HETE-mediated events". Inflammation. 19 (2): 193–205. doi:10.1007/bf01534461. PMID 7601505.
  11. Muñoz-Garcia A, Thomas CP, Keeney DS, Zheng Y, Brash AR (March 2014). "The importance of the lipoxygenase-hepoxilin pathway in the mammalian epidermal barrier". Biochimica et Biophysica Acta. 1841 (3): 401–8. doi:10.1016/j.bbalip.2013.08.020. PMC 4116325. PMID 24021977.
  12. 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 Krieg P, Fürstenberger G (March 2014). "The role of lipoxygenases in epidermis". Biochimica et Biophysica Acta. 1841 (3): 390–400. doi:10.1016/j.bbalip.2013.08.005. PMID 23954555.
  13. 13.0 13.1 Zheng Y, Yin H, Boeglin WE, Elias PM, Crumrine D, Beier DR, Brash AR (July 2011). "Lipoxygenases mediate the effect of essential fatty acid in skin barrier formation: a proposed role in releasing omega-hydroxyceramide for construction of the corneocyte lipid envelope". The Journal of Biological Chemistry. 286 (27): 24046–56. doi:10.1074/jbc.M111.251496. PMC 3129186. PMID 21558561.
  14. Kuhn H, Banthiya S, van Leyen K (April 2015). "Mammalian lipoxygenases and their biological relevance". Biochimica et Biophysica Acta. 1851 (4): 308–30. doi:10.1016/j.bbalip.2014.10.002. PMC 4370320. PMID 25316652.
  15. Jobard F, Lefèvre C, Karaduman A, Blanchet-Bardon C, Emre S, Weissenbach J, Ozgüc M, Lathrop M, Prud'homme JF, Fischer J (January 2002). "Lipoxygenase-3 (ALOXE3) and 12(R)-lipoxygenase (ALOX12B) are mutated in non-bullous congenital ichthyosiform erythroderma (NCIE) linked to chromosome 17p13.1". Human Molecular Genetics. 11 (1): 107–13. doi:10.1093/hmg/11.1.107. PMID 11773004.
  16. Eckl KM, Krieg P, Küster W, Traupe H, André F, Wittstruck N, Fürstenberger G, Hennies HC (October 2005). "Mutation spectrum and functional analysis of epidermis-type lipoxygenases in patients with autosomal recessive congenital ichthyosis". Human Mutation. 26 (4): 351–61. doi:10.1002/humu.20236. PMID 16116617.
  17. Baer AN, Klaus MV, Green FA (February 1995). "Epidermal fatty acid oxygenases are activated in non-psoriatic dermatoses". The Journal of Investigative Dermatology. 104 (2): 251–5. doi:10.1111/1523-1747.ep12612793. PMID 7829882.
  18. Spector AA, Kim HY (January 2015). "Discovery of essential fatty acids". Journal of Lipid Research. 56 (1): 11–21. doi:10.1194/jlr.R055095. PMC 4274059. PMID 25339684.

Further reading

External links